1. Field
The present disclosure relates generally to sonar systems and, in particular, to continuous active sonar sonobuoys. Still more particularly, the present disclosure relates to an apparatus and method for detecting and locating underwater targets using continuous active sonar sonobuoys.
2. Background
Sonar, an abbreviation for sound navigation and ranging, is a technique that uses sound propagation for navigation, communications, and/or the detection of underwater objects. As used herein, “underwater” means under the surface of the water. Oftentimes, sonar is used for acoustically locating objects of interest in the water. These objects of interest may be vessels, such as, for example, submarines. An object of interest, as used herein, may be referred to as a “target.”
A sonobuoy is a type of sonar device that can be ejected from an aerial vehicle or a water vehicle in a container and then deployed from the container upon impact with the water. Both passive sonobuoys and active sonobuoys may be used for target detection. A passive sonobuoy emits no sound into the water. Rather, a passive sonobuoy listens for sound. In response to detecting sound, the receiver may generate data that is then sent back to the vehicle using, for example, radio communications.
An active sonobuoy emits sound in the form of a pulse wave into the water and listens for the returning echo. As used herein, an “echo” is the reflection of the pulse wave off a target. In other words, the pulse wave emitted by a transmitter in the active sonobuoy may rebound off a target and then be detected by a receiver in the active sonobuoy as an echo. Oftentimes, the pulse wave emitted by the active sonobuoy has a low duty cycle of below about 20 percent. Once an echo is received, the receiver may transmit data to a processor onboard the vehicle using, for example, radio communications.
A continuous active sonar (CAS) sonobuoy may be capable of emitting a pulse wave having a high duty cycle of about 100 percent. In other words, the pulses in the pulse wave may be emitted continuously. An array of continuous active sonar sonobuoys may be positioned within a particular region of water for use in detecting targets. However, the number of continuous active sonar sonobuoys that may be used may be limited by cross-channel interference. Further, the size of the region in which a target may be detected may be limited by the number of sonobuoys that can be used. Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above, as well as other possible issues.